Active NaCl transport in the proximal convoluted tubule is electroneutral and transcellular. The mechanism of apical NaCl transport and basolateral chloride exit is unknown. Apical NaCl transport has been proposed to occur via either parallel Na+/H+ and Cl-/OH- (or HCO3 ion) antiporters or a NaCl symporter. Basolateral chloride exit has been proposed to occur via a chloride conductance, a Cl-/OH- (or HCO3 ion) antiporter or via a KCl symporter. The purpose of the first part of these proposed studies is to examine the mechanism of apical NaCl entry and basolateral chloride exit in the proximal convoluted tubule using in vitro microperfusion. The second part of the project has been designed to investigate the regulation of active NaCl transport in the proximal convoluted tubule. Catecholamines, angiotensin II and atrial natriuretic factor exert a large effect on volume absorption in the proximal tubule. These substances may have an important role in regulating proximal tubular solute transport independent of their hemodynamic effect. Peritubular protein has been shown to modulate neutral active NaCl transport in the proximal convoluted tubule, but does not affect the active or passive transport of other solutes. Other substances which affect proximal tubule transport may also modulate the transport of specific solutes. These studies will examine whether catecholamines, angiotensin II and atrial natriuretic factor have a nonspecific effect on solute transport or whether they modulate the transport of specific solutes in the proximal tubule. It is possible that, as with peritubular protein, they specifically modulate neutral active NaCl transport. These proposed studies will provide a better understanding of the mechanism regulation of active NaCl transport in the proximal tubule. As a postdoctoral fellow, I worked in Dr. Floyd C. Rector's laboratory at the University of California, San Francisco. Dr. Rector provided me with a strong foundation in renal physiology. In July, 1984, I joined the pediatrics faculty at the University of Texas Health Science Center at Dallas. I am conducting my research in Dr. Juha P. Kokko's laboratory. Dr. Kokko, the sponsor of my grant, has provided me with an ideal environment in which to perform my research. His support and guidance will be invaluable during the course of these studies.